Choosing a boundary-layer parameterisation for tropical cyclone modelling

The boundary layer in a tropical cyclone is in some respects unlike that elsewhere in the atmosphere. It is therefore necessary to evaluate boundary-layer parameterisations for their suitability for use in tropical cyclone simulation. Previous work has shown substantial sensitivity to the choice of scheme and identified specific shortcomings in some schemes, but without recommending which schemes are most suitable. Here, several schemes, representative of those available in popular modelling systems, are reviewed and applied in a simplified modelling framework. Based on a comparison with observations and on theoretical grounds, one popular class of schemes is shown to be badly flawed in that it incorrectly predicts the near-surface wind profile, and therefore should not be used. Another is shown to be sensitive to diagnosis of the boundary-layer depth, a difficult problem in the core of the tropical cyclone, and caution is advised. The Louis boundary-layer scheme and a higher-order closure scheme are, so far as we can discern, without major problems, and are recommended. The recommendations and discussion herein should help users make a more informed choice of boundary-layer parameterisation, and to better understand the results that they obtain.